1. Technical Field
The present invention relates to a ring oscillator, a clock signal generation circuit, and so on.
2. Related Art
As an oscillation circuit for generating a clock signal with a predetermined frequency, there is well known a ring oscillator having a plurality of delay elements connected to each other in a ring-like manner (see e.g., JP-A-2011-61462).
As another oscillation circuit, a temperature compensated crystal oscillator (TCXO) is also known well. In comparison between the ring oscillator circuit and the TCXO, the TCXO is superior in frequency accuracy, but in low power consumption, the ring oscillator circuit is superior. Therefore, which is used as the generation circuit of the clock signal is determined depending on the electronic apparatus to be applied.
Incidentally, clock signals are used in all electronic apparatuses, and among them, a positioning satellite signal receiver represented by a GPS (Global Positioning System) receiver can be said to be a good example requiring a highly accurate clock signal. This is because the clock signal is directly linked to the performance of the electronic apparatus, and in the case of the positioning satellite signal receiver, the accuracy of the clock signal directly effects the positioning accuracy. On the other hand, in the case of an electronic apparatus operating with a battery, in order to make long hours of operation possible, reduction of the power consumption is required. Therefore, it is also desirable in generation of the clock signal that the power consumption is as low as possible. Also in the positioning satellite signal receiver described above, since such a receiver is configured as a portable or small-sized electronic apparatus operating with a battery in many cases, the reduction of the power consumption is one of important matters. In comparison between the ring oscillator circuit and the TCXO as a generation circuit of the clock signal, there has been a problem that the ring oscillator circuit is lower in power consumption, but is lower in frequency accuracy of the clock signal, and the TCXO is higher in frequency accuracy of the clock signal, but is higher in power consumption.
In particular, as a problem of the frequency accuracy of the clock signal generated by the ring oscillator circuit, there has been the following problem. That is, since the related-art ring oscillator circuit is configured by connecting a plurality of delay elements having a uniform delay amount to each other in a ring-like manner, it is theoretically possible to improve the frequency accuracy of the clock signal if using the delay elements smaller in delay amount.
However, since reduction of the delay amount depends on the miniaturization manufacturing technology for a semiconductor, there is a technical limitation. Further, since the smaller the delay amount of the delay element is, the higher the manufacturing cost is, the semiconductor circuit manufactured using the miniaturization manufacturing technology, namely the delay element small in delay amount, is high in manufacturing cost, and is expensive.